The controller for a brushless motor may be configured such that, when the supply voltage used to power the controller drops below a brown-out threshold, the controller resets itself. This then has the advantage that, when the controller is powered off, the controller resets itself in readiness for power on.
A problem with this arrangement is that, as the supply voltage begins to drop following a power off, the controller may behave erratically before the supply voltage reaches the brown-out threshold. In order to solve this problem, the controller may be configured to monitor an input voltage and halt operation should the input voltage drop below an under-voltage threshold. The under-voltage threshold is then set such that controller halts operation at a higher supply voltage than that of the brown-out threshold. Once operation is halted, the controller waits until such time as the supply voltage drops below the brown-out threshold, at which point the controller resets itself.
A problem with this arrangement is that it may take a relatively long period of time (e.g. several seconds) after the input voltage has dropped below the under-voltage threshold before the supply voltage drops below the brown-out threshold. During this time it is not possible to restart the controller. Accordingly, should an attempt be made to power on the controller, the controller will fail to restart. Worse, if an attempt is made to power on the controller, the supply voltage will actually rise and thus fail to drop below the brown-out threshold.